1. Field of the Invention:
This invention relates in general to the drill string of a rotary drilling rig, and in particular to a mechanism for reducing the torque required to break-out a joint.
2. Description of the Prior Art:
In U.S. Pat. No. 4,658,915, Apr. 21, 1987, Gregg A. Goris, et al, a reduced torque break-out assembly is shown. The assembly has an upper sub with a collar located around pin threads. The box end of a joint of drill pipe secures to the pin threads and the upper edge or shoulder on the box engages a shoulder on the collar. These shoulders make up to a high torque because of the friction between the shoulders.
A pair of ramp rings are located between the collar and the upper sub. The ramp rings have mating upper and lower inclined surfaces. One of the ramp rings is fixed to the upper sub to rotate with it. The other ramp ring is fixed to the collar to rotate with it. When left hand torque is applied, the upper ring will slide slightly along the inclined ramp surfaces relative to the lower ring. This allows the collar to move axially a slight distance up the upper sub. This reduces the friction between the mating shoulders of the collar and the box end of the drill pipe. A split ring extending around the ramp rings expands during the ramping motion, then contracts to reset the rings.
While this assembly is satisfactory, occasions exist in which one may not wish to allow the assembly to break-out at the reduced torque. For example, in the case of drilling with a high potential of drill string backlash, the backlash could accidentally cause the assembly to loosen due to the reduced torque.